This invention relates to display systems. The invention has particular, although not exclusive, relevance to display systems including a projection system in which light from a light source is modulated by a spatial light modulator device, the modulated light then being projected onto a projection screen.
Spatial light modulator devices suitable for use in such projection system may take several forms.
One example of a spatial light modulator device is a liquid crystal device comprising a matrix of individually addressable liquid crystal pixels. Such spatial light modulators may act either in a transmissive mode in which the light passes through the pixels of the liquid crystal device, or in a reflective mode in which the light is reflected by each pixel of the liquid crystal device.
Another example of a spatial light modulator device is a deflectable mirror device (DMD) which comprises an array of mirrored cantilever beam structures, each structure carrying an electrode so as to be electrostatically deflectable between two positions. Thus, dependent on the electric field applied to the device, each mirrored structure will reflect an incident light beam into two alternative light paths, either towards an optical system for projection onto a projection screen, or alternatively into a beam dump. Using an array of such structures, each structure being individually addressable by part of the incoming light beam, the incoming light beam can be spatially modulated with a two dimensional image which can then be projected onto the projection screen.
Known projection systems in which light from a light source is modulated by a spatial light modulator device suffer the disadvantage that there is often a limit in the amount of light flux which can be directed onto the spatial light modulator. This limit is caused by, for example limitations associated with the heating effect of the radiant flux, or saturation due to a high luminous flux. Where projection systems are limited in light output, two or more projection systems may be xe2x80x9cstackedxe2x80x9d by placing the projection systems adjacent to each other such that the projected images are superimposed on the projections screen, producing an overall bright image. However, such an arrangement is both inefficient and space consuming.
U.S. Pat. No. 5,035,475 discloses a display system comprising two spatial light modulators in the form of an array of movable mirrors. Baffles in the form of rows of parallel slits are interposed in the light path between the light source and the two mirror arrays. A beam splitter is effective to split light from the light source between the two mirror arrays, and to recombine light reflected along the normals to the mirror arrays. The baffles are effective to absorb light which is reflected along other directions. By using the two mirror arrays, the images produced by the two arrays may be interleaved to remove dark stripes in the projected images which are produced by the two baffles. However in such arrangement the flux of the light in the final projected image is still limited by the flux of light produced by each mirror array.
Problems also occur in colour projection systems comprising one or more spatial light modulator devices. In order to achieve a colour projection system it is known to split the incoming light by one or more spectral splitting devices, for example, dichroic mirrors into three primary colour channels. An example of such a prior art system is shown in FIG. 1 which is a schematic diagram of an overview of a colour projection system using three spatial light modulators in the form of DMDs.
Referring to FIG. 1, the particular example of a display system to be described is arranged to project a colour image onto a display screen 101. The display system includes a light source 101 arranged such that the beam from the source is directed onto three planar deflectable mirror display devices 105,107,109 described.
Positioned in the light path between the light source 103 and the first deflectable mirror device 105 are two dichroic mirrors 111,113. The first dichroic mirror 111 is designed and angled to reflect blue light onto the second planar deflectable mirror display device 107 and transmit all other incident light. The second dichroic mirror 113 is designed and angled so as to reflect red light onto the third planar deflectable mirror device 109 and transmit the remaining green component of the light from the source 103 onto the first deflectable mirror display device 105.
The three deflectable mirror devices 105,107,109 are arranged to be capable of reflecting the three colour components of the beam from the source 103 so as to direct the spatially modulated beam through a projection lens 115 onto the display screen 101.
However such arrangements do not take account of the fact that the luminous flux of the various spectral components, for example the primary colours red, green and blue within white light, is unequal.
It is an object of the present invention to provide a display device in which the above problems of limited output light are at least alleviated.
According to a first aspect of the present invention there is provided a display system comprising a plurality of spatial light modulators and including extra spatial light modulators designed to increase the total light flux spatially modulated by the modulators.
According to a second aspect of the present invention there is provided a display system comprising: a light source; at least two spatial light modulators; means for splitting light of the same spectral composition from the light source between the spatial light modulators; means for combining spatially modulated light produced by the spatial light modulators; and means for displaying the combined light such that the combined light is of greater light flux than the light produced by any of the spatial light modulators.
According to a third aspect of the present invention there is provided a display system comprising: a multi wave length light source; a plurality of spatial light modulators; wavelength selection means for splitting light of different spectral composition between the spatial light modulators; means for combining spatially modulated light produced by the spatial light modulators; and means for displaying the combined light; wherein there are provided sufficient spatial light modulators to increase the balance of the division of the light flux produced by the light source between the spatial light modulators.
The means for displaying suitably comprising means for projecting the combined light onto a projection screen.